This invention relates to sound absorbing and shielding structures for automotive vehicles to attenuate noises in passenger compartments of the automotive vehicles and, more particularly, to a structure and method of absorbing and shielding sound at a remarkably improved sound shielding performance.
In general, sound absorbing and shielding materials have been employed in various areas of a house, a railway vehicle, an air craft and an automotive vehicle but are restricted by various conditions in dependence on the mounting areas. Especially in the automotive vehicle""s application, restrictions involve a large amount of restrictive conditions in weight and space etc. It is thus required to provide the sound absorbing and shielding material which is light in weight and less in space.
For example, extensive research and development work has been undertaken in a dash insulator, which is composed of a sound absorbing section and a cover section, of the automotive vehicle to improve a performance of the sound absorbing and shielding structure by merely increasing the weight of the sound absorbing section and the cover section. Also, in the application of particular sound absorbing and shielding material, natural fibers such as a felt in the form of a layer is located in an area where sound shielding effect is needed, with the amount of such usage being increased with a view to improving the performance.
However, such a technique for merely increasing the weight of the sound absorbing material encounters a less improvement in the sound absorbing and shielding performance despite an increase in production cost with a resultant degraded performance especially in a low frequency area below 500 Hz. In addition, when it is required to further improve the performance with the use of presently employed components, the sound absorbing material is inevitably caused to increase in weight and volume, resulting in a deteriorated fuel consumption against a worldwide trend in the protection of environment. Thus, there is an increasing demand for improving performance of the sound absorbing and shielding structure.
The present invention has been made with a view to meeting the increasing demand in the related art and it is therefore an object of the present invention to provide a sound absorbing and shielding structure which is light in weight and is superior in a sound absorbing and shielding performance and which is specifically suited for use as a sound absorbing and shielding material of an automotive vehicle.
It is another object of the present invention to provide a method of absorbing and shielding sound from a source of sound at a highly improved sound absorbing and shielding performance.
According to a first aspect of the present invention, there is provided a sound absorbing and shielding structure which comprises at least four layers including a first panel layer, a sound absorbing material layer, and a second panel layer, which are located in a sequence from a source of sound, and wherein the first panel layer has a ventilating property.
With such a structure, the sound is first transmitted through the sound absorbing material layer and is incident on the second panel layer by which the sound is reflected back to the sound absorbing material layer again to be effectively absorbed thereby, resulting in a remarkably improved sound absorbing and shielding performance which is far superior to the related art practice.
According to a second aspect of the present invention, there is provided a sound absorbing and shielding structure which comprises first panel layer means located adjacent a source of sound, sound absorbing layer means fixedly supported by the first panel layer means, and second panel layer means spaced from the first panel layer means to define an air layer between the first and second panel layer means, wherein the sound absorbing layer means has a ventilating property.
According to a third aspect of the present invention, there is provided a method of absorbing and shielding sound from a source of sound, which comprises locating a first panel layer at a position adjacent a source of sound, fixing a sound absorbing material layer, which has a ventilating property, onto the first panel layer,
locating a second panel layer in a spaced relationship relative to the first panel, and defining an air layer between the first and second panel layers.